Add decorators in swf.exceptions and use them in swf.models

- Parametrized decorators with a single responsibility.
- Fix the unit tests.
- Fix the doctests.
- Wrap methods that may raise unknown resource errors.
Merge pull request #36 from botify-labs/fix/unknown-resource-handling

Fix/unknown resource handling
Bump version to 0.1.36
Fix WorkflowExecution.signal(): fix empty input
Bump version to 0.1.37